1. Field of the Invention
The invention generally relates to a product for controlling dissolving rate of orthopedic implant material and a manufacture process that diffuses a treatment solution into biomedical orthopedic implant material to form a second phase on the implant material at constant temperature and humidity.
2. Description of the Related Art
Bone aging and osteoporosis are common cases in clinics of orthopedics. Bone substitutes are increasingly in urgent need as the population of old ages increases, bone substitutes. Bone damages caused by disease or trauma can be recovered by partially filling up bone filling material. The bone filling material includes autograft material, allrgraft material and processed animal bone. Among those, orthopedic implant cement based calcium sulfate, such as Collagrant and OSTEOSET Bone Graft susbstutites, has been used commonly. However, it has some disadvantages such as non-availability, self-repelling, infection, need of second surgery, too fast dissolving rate, growth of soft fiber tissues. In addition, complicate human bone structure and stress generated accordingly when bone recovery proceeds limit the application of those bone substitutes in use. Therefore, how to avoid the need of second surgery, lowering loss rate of implant material as substitutes and promote growth of bone cells are key issues to study in the field. Keeping the loss rate of bone filling material as close to the bone growth rate helps avoid the presence of fiber tissues. Bone filling material is an implant material, including single material or composite, which promotes the bone recovery in osteogenic, osteoinductive or osteoconductive ways. The bone filling material is divided into three main categories of autograft, allrgraft, xenograft and synthetic materials and blends thereof, according to its functional construction. The synthetic material includes osteoconductive blocks or granules, osteoconductive cement, osteoinductive proteins and composites.
The appearance of synthetic materials broadens the application of the bone filling material. The synthetic material can be also classified into two main categories: ceramics and polymers. The ceramic synthetic material is mainly based on either calcium phosphate or calcium sulfate, both of which have good bio-compatibility and are absorbable in vivo. Examples of the polymeric synthetic material are PMMA which cannot be absorbed in vivo, and PLLA which can be absorbed in vivo. Calcium sulfate, so-called gypsum, includes calcium sulfate anhydrate (CaSO4), calcium sulfate hemihydrate (CaSO4.½H2O) and calcium sulfate dihydrate (CaSO4.2H2O). High-hardness gypsum most commonly used for medical purpose is calcium sulfate hemihydrate which generate crystalline water and turns into calcium sulfate dihydrate to offer solidification after meets water. The chemical scheme is as follows:CaSO4.½H2O+ 3/2H2O—CaSO4.2H2O
During the reaction, more water, in addition to what is needed for solification, is needed for stirring thoroughly reactants. The more water adds into, the much time of solification needs. After the reaction completes, excess of water still remained inside the structure of calcium sulfate distills into vapors and voids form accordingly. Therefore, the more water adds in, the weaker of the structural strength of calcium sulfate becomes. Calcium sulfate hemihydrate is obtained by dehydrating calcium sulfate dihydrate by heat. Calcium sulfate hemihydrate with inherent humidity-absorbance can be used to control the crystallization of calcium sulfate dihydrate reduced from calcium sulfate hemihydrate to get stronger products. Calcium sulfate hemihydrate can be divided into a, (3 types of hemi-calcium sulfates according to its physical properties.
The inventors have intensively studied on controlling loss rate of the bone filling material as close to growth rate of bone using calcium sulfate, while avoiding the need of second surgery, avoiding the growth of promoting the growth of osteocells.